Spherical and non-spherical bubbles in cosmological phase transitions

TL;DR

This paper investigates how different bubble geometries during cosmological phase transitions affect plasma perturbations and gravitational wave production, highlighting that geometry has a limited impact on plasma perturbations.

Contribution

It provides a comparative analysis of spherical, cylindrical, and planar bubble walls, deriving analytical expressions for bulk kinetic energy and discussing implications for gravitational wave generation.

Findings

Different bubble geometries produce similar plasma perturbations.

Analytical expressions for kinetic energy in planar walls are derived.

Implications for gravitational wave signals are discussed.

Abstract

The cosmological remnants of a first-order phase transition generally depend on the perturbations that the walls of expanding bubbles originate in the plasma. Several of the formation mechanisms occur when bubbles collide and lose their spherical symmetry. However, spherical bubbles are often considered in the literature, in particular for the calculation of gravitational waves. We study the steady state motion of bubble walls for different bubble symmetries. Using the bag equation of state, we discuss the propagation of phase transition fronts as detonations and subsonic or supersonic deflagrations. We consider the cases of spherical, cylindrical and planar walls, and compare the energy transferred to bulk motions of the relativistic fluid. We find that the different wall geometries give similar perturbations of the plasma. For the case of planar walls, we obtain analytical expressions for the kinetic energy in the bulk motions. As an application, we discuss the generation of gravitational waves.